The answer to 'why is my dimmer switch tripping breaker' is that a dimmer switch overloading the circuit is a common cause. Dimmer switches have a maximum wattage rating, and if the lights connected to it exceed that rating, it can cause the circuit breaker to trip. This is a safety feature to prevent overloading and potential fire hazards.
Other potential causes include a faulty dimmer switch, loose wiring, or a problem with the circuit itself. If the dimmer switch is old or damaged, it may not be able to handle the electrical load, causing the breaker to trip. Loose wiring can also create a short circuit, leading to the breaker tripping.